Two-part dental compositions with self-cure mechanisms are currently being used as adhesives, cavity liners/bases, filling materials, endodontic sealers, or cements. The benefits for having a self-cure mechanism include unlimited depth of cure and the ability to cure in areas where there is limited or no light access. When the two parts are mixed together, the mixed composition will self-cure or harden on its own. The self-curing mechanism can be ionically through acid-base reaction, free-radically through a redox initiator system comprising a reducing agent and an oxidizing agent, or a combination of both. In addition to a self-curing mechanism, a photo-initiator can also be incorporated in the composition to make it also light-curable. The above three curing mechanisms can be used singularly or in combination so the two-part composition can be self-curable, dual-curable, or tri-curable. Examples of ionically curable compositions include zinc phosphate cement, zinc carboxylate cement, glass ionomer cement/liner/filling material/sealant, and resin-modified glass ionomer cement/liner/filling material/sealant. Examples of free-radically curable compositions incorporating a redox-initiator system include self-cure or dual-cure resin cement, composite filling material, core buildup materials, adhesive, cavity liner/base, endodontic sealer, and endodontic filling material. A photo-initiator can be included to make these compositions dual-curable (i.e. both self-curable and light-curable). Some systems such as resin-modified glass-ionomers can be tri-curable, i.e. having all-three curing mechanisms: ionically, free-radically through a redox initiator and free-radically through a photo-initiator.
It is often desirable to impart additional functionality to the above two-part dental compositions besides the basic function of restoring defective dentition. The additional functionality can be achieved by incorporating one or more functional chemicals or compounds. The list of functional chemicals/compounds includes a redox indicator, a pH indicator, a photobleachable dye, an acidic compound, a fluorescent compound, a fluoride releasing agent, an antimicrobial compound, or a combination of above. These functional chemicals/compounds impart a special property to the composition or aid the dentist in carrying out the restorative procedures.
However, stability issues can arise when these functional chemicals or compounds are incorporated into a two-part self-cure, dual-cure or tri-cure composition as at least one of the following issues may exist: (1) the functional chemical is not stable in the presence of the redox initiator (free-radically curing) or acid/base (ionically curing) of the two-part composition so that the functional chemical loses its intended function; (2) the redox initiator (free-radically curing) or acid/base (ionically curing) of the two-part composition is not stable in the presence of the functional chemical, causing shelf-life stability issues; and/or (3) the functional chemical interacts with the redox initiator (free-radically curing) or acid/base (ionically curing) of the two-part composition, forming an unacceptable coloration or color change during storage prior to use.
There is thus a need for a dental material that includes a special functionality without unintended instability of one component in the presence of another or premature reactions therebetween.